In the pollution control field, several approaches are used to remove sulfur oxides and other contaminants from a flue gas produced by the burning of a fossil fuel in order to comply with both European and U.S. emissions requirements.
One approach involves locating and utilizing fossil fuels lower in sulfur content and/or other contaminants. A second approach involves removing or reducing the sulfur content and/or other contaminants in the fuel prior to combustion of the fuel. Such may be achieved through mechanical and/or chemical processes. A major disadvantage to this second approach is the limited cost effectiveness of the mechanical and/or chemical processes required to achieve the mandated levels of reduction of sulfur oxides and/or other contaminants.
By and large, the most widely used approaches to removing sulfur oxides and/or other contaminants from flue gas involve post-combustion clean up of the flue gas. Several methods have been developed to remove SO2 species from flue gases.
One method for removing SO2 from flue gas involves either mixing dry alkali material with the fuel prior to combustion, or injection of pulverized alkali material directly into the hot combustion gases to remove sulfur oxides and other contaminants via absorption or absorption followed by oxidation. Disadvantages of this method include: fouling of heat transfer surfaces; low to moderate removal efficiencies; poor reagent utilization; and increased particulate loadings in the combustion gases which may require additional conditioning of the gas if an electrostatic precipitator is used for down stream particulate collection.
Another method for removing SO2 from flue gas, collectively referred to as wet chemical absorption processes and also known as wet scrubbing, involves “washing” the hot flue gases with an aqueous alkaline solution or slurry in an up-flow, gas-liquid contact device to remove sulfur oxides and other contaminants. Disadvantages associated with wet scrubbing processes include: the loss of liquid both to the atmosphere and to the sludge produced in the process; and the economics associated with the construction materials for the absorber module itself and all related auxiliary downstream equipment, such as primary/secondary dewatering and waste water treatment subsystems.
Still another method for removing SO2, collectively referred to as spray drying chemical absorption processes and also known as dry scrubbing, involves spraying an aqueous alkaline solution or slurry which has been finely atomized via mechanical, dual-fluid or rotary cup-type atomizers, into the hot flue gases to remove sulfur oxides and other contaminants. Disadvantages associated with these dry scrubbing processes include: moderate to high gas-side pressure drop across the spray dryer gas inlet distribution device; and limitations on the spray down temperature required to maintain controlled operations.
Other known systems for SO2 removal from flue gas require additional equipment, are very complicated in design and operation, and/or provide a very costly removal method. It is thus apparent that a simple and economical method and system is needed to remove SO2 from flue gas in general, and particularly to remove SO2 from flue gas produced by the burning of waste, that overcomes the disadvantages of these prior approaches used in fossil fuel combustion fields.